New No. 1 Rafael Nadal has won 10 titles this year, including two majors. (Feng Li/Getty Images)

With Rafael Nadal back at No. 1 for the first time in more than two years, Roger Federer applauded his longtime rival for a dominant season that followed a lengthy injury layoff.

"An unbelievable comeback. No doubt about it," Federer said. "One year ago, people were saying he might never play tennis again. One year later, he's world No. 1. That's how quick things can go in tennis, which is great."

Nadal began his season in February after missing seven months with a knee injury. Since then, the 27-year-old Spaniard is 65-4 with 10 titles, including his eighth French Open and second U.S. Open. Other than a first-round loss at Wimbledon, Nadal has made the final of all 14 of his tournaments.

"I'm really happy that Rafa's proved that you never write off someone like him," Federer said. "[H]e proved himself so many times this year that he deserves to be world No. 1."